Continuing his work in the theatre through the 1990s, both as an actor and a director, Rees was awarded an Obie Award for his 1992 performance in the Off-Broadway play The End of the Day. In 1995 he was nominated for a Tony Award for Best Actor in a Play for his role in Indiscretions.[4][6] He recorded many audiobooks, including Memnoch the Devil by Anne Rice.[7]

In 2014, Rees directed Dog and Pony, a musical written by Rick Elice and Michael Patrick Walker, which had its world premiere at the Old Globe Theatre in San Diego.

His last role was as Anton Schell in the musical version of The Visit, opposite Chita Rivera, which opened on Broadway on 23 April 2015 and closed on 14 June 2015.[11] Rees left the production in May 2015 due to his illness.[12]

Rees was to have directed a new musical written by Elice and Will Van Dyke, Magnificent Climb, in the fall of 2016 at MCC Theater in New York. He was also scheduled to perform his one-man Shakespeare show, What You Will in New York in the autumn of 2015, and had hoped to return to the Royal Shakespeare Company for a stint in Don Quixote in 2016.

Rees had lived in the United States for more than 25 years;[2] he became a naturalised U.S. citizen in 2009.[5] He converted to Judaism in the 1980s.[13] Rees married his partner of 33 years, playwright Rick Elice, in 2011.[14][15][16] Rees and Elice also collaborated professionally, including as co-playwrights of the comedic thriller Double Double.[17] Elice co-wrote (with Marshall Brickman) the libretto for The Addams Family musical, the cast of which Rees had joined on 22 March 2011. In 2012, Elice and Rees received Tony Award nominations for Elice's stage adaptation and Rees' co-direction (with Alex Timbers), respectively, of Peter and the Starcatcher.[4]

After a diagnosis of brain cancer in October 2014, Rees focused his energy on his commitment to playing opposite Chita Rivera on Broadway in The Visit, the final musical written by John Kander and Fred Ebb. While undergoing two brain surgeries, two courses of radiation and ongoing chemotherapy, Rees managed to rehearse, preview and open in The Visit on 23 April 2015. By the middle of May, it had become too difficult for him to speak, and he left the show. Rees died of brain cancer at age 71 at his home in New York on 10 July 2015. On Wednesday, 15 July 2015, the marquee lights at all the theatres on Broadway were dimmed in his honour.[18] His ashes were sprinkled into the Atlantic Ocean. Two months later, there was a memorial service for him at Broadway's New Amsterdam Theatre.[19]